Learn Hardcore Croatian: Večeras sam potpuno umoran.

This short form sam is a clitic, and clitics normally go in the second position in the clause, not at the very beginning. That’s why the sentence is:

Večeras sam potpuno umoran.
(literally: Tonight am completely tired.)

You cannot start the sentence with sam:

✗ Sam večeras potpuno umoran. – ungrammatical.

If you add the pronoun ja, it normally goes before sam:

Ja sam večeras potpuno umoran. – I am completely tired tonight. (emphasis on I)

Why is there no word for I in the sentence? Where is the subject?

The subject I is included in the verb form sam.

Croatian is a pro‑drop language: subject pronouns (like ja = I) are usually omitted because the verb ending already shows the person:

sam = (I) am
si = (you) are
je = (he/she/it) is

So:

Večeras sam potpuno umoran. – ja is understood from sam.
Ja sam večeras potpuno umoran. – same meaning, but ja adds emphasis: I (as opposed to others) am tired tonight.

Why is it umoran and not umorna or umorno?

Umoran is an adjective meaning tired. In Croatian, adjectives must agree with the gender, number, and case of the noun (or the understood subject).

Here the subject is ja (I) and is understood as:

masculine singular, so the adjective must be masculine singular nominative: umoran.

Other forms:

umorna – feminine singular (for a woman speaking)
- Večeras sam potpuno umorna. – said by a woman
umorno – neuter singular (for neuter nouns, e.g. dijete je umorno – the child is tired)

So if a woman said this sentence about herself, she would normally say:

Večeras sam potpuno umorna.

Can I change the word order? For example: Večeras sam umoran potpuno or Potpuno sam večeras umoran?

Croatian word order is more flexible than English, but not every order sounds natural.

These are natural:

Večeras sam potpuno umoran. – neutral, most typical.
Večeras sam jako umoran. – replacing potpuno with another adverb, but same pattern.
Ja sam večeras potpuno umoran. – extra emphasis on I.
Potpuno sam umoran večeras. – possible, slightly more emphasis on potpuno or on the contrast with other times.

These sound unnatural or wrong:

Večeras sam umoran potpuno. – sounds off; adverbs like potpuno normally come before the adjective.
Sam večeras potpuno umoran. – sam cannot be in first position; clitics avoid starting the clause.

General rules here:

Keep sam near the beginning (second position).
Put potpuno directly before the adjective umoran.

What exactly does potpuno mean, and how is it different from vrlo or jako?

Potpuno means completely / totally / entirely.

Večeras sam potpuno umoran.
– I am completely exhausted / totally tired tonight.

Other common adverbs with umoran:

vrlo umoran – very tired (a bit more neutral/formal)
jako umoran – very/really tired (very common in speech)
strašno umoran – terribly/extremely tired (colloquial, stronger)

Nuance:

potpuno umoran suggests you are 100% tired, with a sense of total exhaustion.
vrlo/jako umoran means very tired, but not necessarily “completely done for”.

Can I say noćas instead of večeras? Is there a difference?

Both relate to the later part of the day, but there is a nuance:

večeras – this evening / tonight (focus on evening time, roughly after work until late evening).
noćas – tonight with more focus on the night, often the late night / sleeping period.

In your sentence:

Večeras sam potpuno umoran. – You’re talking about how tired you are this evening.
Noćas sam potpuno umoran. – Could be used, but more naturally you’d say this in a context involving the night (e.g. I’m completely tired tonight, so I’ll sleep early / I can’t go out late).

For a neutral “tonight” about your current state in the evening, večeras is the best choice.

Is umoran a verb form like a past participle, or is it just an adjective?

In modern usage, umoran is treated as a regular adjective meaning tired.

It behaves like other adjectives:

It changes for gender: umoran / umorna / umorno
It can be graded: umorniji (more tired), najumorniji (most tired)
It can modify nouns: umoran čovjek (a tired man), umorna žena, etc.

The verb related to this state is:

umoriti (se) – to tire (someone) / to get tired

But in Večeras sam potpuno umoran., umoran is simply an adjective linked to sam (I am).

How would I make this sentence negative? How do I say I’m not completely tired tonight?

To negate sam, you use the negative form nisam (I am not).

So:

Večeras nisam potpuno umoran.
– Tonight I’m not completely tired.
(masculine speaker)
Večeras nisam potpuno umorna.
– same meaning, feminine speaker.

Structure:

Večeras (time) + nisam (I am not) + potpuno (completely) + umoran/umorna (tired).

How do you pronounce večeras and umoran? Where is the stress?

Approximate pronunciation using English sounds:

večeras: /veˈtʃe.ras/
- ve – like ve in very
- če – like che in check
- ras – ras as in Russ
- Main stress on the second syllable: ve-ČE-ras
umoran: /ˈu.mo.ran/
- u – like oo in food (but shorter)
- mo – mo as in motel
- ran – run but with a trilled/flapped r and clear a
- Main stress on the first syllable: U-mo-ran

Remember: Croatian has a rolled/trilled r, and vowels are pure and short, not diphthongs.

Is this sentence formal or informal? Can I use it with a doctor, a friend, or in writing?

Večeras sam potpuno umoran. is neutral in style:

Fine with friends and family (informal context).
Also completely acceptable in polite or semi‑formal conversation (e.g. telling a doctor how you feel).
It’s neutral enough to be used in written language too (e.g. email: I won’t come because I am completely tired tonight).

You’d only adjust it slightly in very formal writing by adding more context, but the sentence itself is perfectly standard and not slangy.